In the case of a motor vehicle driven by means of an internal combustion engine, in particular by means of a spark-ignition engine, there is the problem that the vapors situated in the fuel tank and laden with hydrocarbons must not be released to the surroundings of the motor vehicle without prior filtering. For this purpose, in motor vehicles, fuel vapor filters, commonly in the form of activated carbon filters, are provided, which are fluidically connected by means of a charging opening of the fuel vapor filter to a tank volume and by means of a ventilation opening of the fuel vapor filter to the internal combustion engine and/or to the surroundings of the motor vehicle. When vapors that escape from the fuel tank are conducted through the fuel vapor filter, hydrocarbons are absorbed and/or adsorbed by the filter material, such that the gas filtered in this way can be released to the surroundings. The filter material laden with hydrocarbons is generally purged by means of intake air of the internal combustion engine, such that hydrocarbons absorbed by means of the filter material are fed to the internal combustion engine. In this way, the absorption capacity of the fuel vapor filter is realized.
During filling of a fuel tank, fuel is introduced into the fuel tank at a rate of up to 60 l/min (liters per minute). Consequently, during the tank filling process, a correspondingly large volume flow of 60 l/min of gas laden with fuel vapors must be conducted through the fuel vapor filter. Here, the fuel vapor filter must be dimensioned such that, even in the case of such high volume flows, hydrocarbons are reliably filtered out by means of the filter material.
During the operation of the motor vehicle, the fuel situated in the fuel tank is subject to movements, such that increasing amounts of hydrocarbons are transferred into the gaseous phase, whereby the internal pressure in the fuel tank increases. In the event of a pressure increase, or an exceedance of a predefined threshold pressure, the fuel tank must be ventilated via the fuel vapor filter, wherein volume flows in the region of 40 l/h (liters per hour) are conducted through the fuel vapor filter.
Even when the motor vehicle is at a standstill, hydrocarbons are transferred into the gaseous phase owing to thermal influences. In this situation, a volume flow in the region of 0.6 l/h prevails in the ventilation of the fuel tank.
A fuel vapor filter must consequently be capable of being operated with widely varying ventilation volume flows from 0.6 l/h to 60 l/min (that is to say six thousand times the ventilation volume flow of 0.6 l/h).
In the case of a high ventilation volume flow of 60 l/min, the gas to be filtered moves, owing to its high kinetic energy and its inertia, on an approximately straight path from the charging opening to the ventilation opening of the fuel vapor filter. Consequently, filter material that is not arranged in the region of a direct connecting line between the charging opening and the ventilation opening within the fuel vapor filter is not impinged on, or is impinged on only to a reduced extent, by the gas to be filtered.
By contrast, in the case of a low ventilation volume flow of 0.6 l/h, an entirely different flow situation prevails within the fuel vapor filter. This is because the gas to be filtered, owing to its relatively high density (in relation to air not laden with hydrocarbons), follows the gravitational force, such that, between the charging opening and the ventilation opening, the gas to be filtered impinges only on filter material in the base region of the fuel vapor filter. By contrast, filter material situated in other regions of the fuel vapor filter is not impinged on, or is impinged on only to a reduced extent, by the gas to be filtered.
WO 2014/016102 A1 describes a fuel vapor filter having a filter housing which has vapor storage regions for receiving filter material. An inlet connector and an outlet connector are provided in the housing, wherein the fuel vapor filter is fluidically connectable via the outlet connector to an internal combustion engine. The fuel vapor filter has a diverting device, by means of which gas flow paths are formed through which the gas to be filtered must flow.
DE 43 20 384 A1 describes an activated carbon filter for fuel tank ventilation. The activated carbon filter has a housing which has a first connector, a second connector and a third connector. Furthermore, the housing has at least two partitions, wherein the partition is arranged between the first connector and the third connector such that gas introduced into the housing by the first connector is diverted by at least the partition in order to be able to emerge from the housing through the third connector.
U.S. Pat. No. 5,538,543 A describes a fuel vapor filter with a housing which has a divided receiving space for receiving an adsorption medium, wherein the respective portions of the receiving space are formed as a lower chamber, middle chamber and upper chamber. The housing has a charging opening and a ventilation opening. Furthermore, the housing has a connection which is open to the atmosphere. The respective portions of the chambers are separated from one another by partitions, wherein holes are provided in each case in the partitions, which holes are arranged so as to be angularly offset with respect to one another, giving rise to a zigzag-shaped gas path during charging of the fuel vapor filter and during purging of the fuel vapor filter.
US 2011/168025 A1 also describes a fuel vapor filter which has an outer container and an inner container arranged within the outer container, wherein the longitudinal axes of the outer container and of the inner container run collinearly with respect to one another. Both in the inner container and in the outer container, there is arranged an adsorption medium in the form of activated carbon, for example.
U.S. Pat. No. 4,717,401 A describes a fuel vapor filter with two connectors. In an interior space of the fuel vapor filter, there are arranged diverting structures which are each cohesively connected to the inner wall of the housing. Consequently, during charging and during purging of the fuel vapor filter, a zigzag-shaped fluid flow is generated within the fuel vapor filter.